Thermal processor



July 9, 1968 N. J. STEVENS 3,391,733

THERMAL PROCESSOR A696597' cl. Sreve/Vs,

IN VEN TOR.

July 9, 1968 N. J. STEVENS 3,391,733

THERMAL PRocEssR Original Filed March .27, 1964 2 Sheets-Sheet 2 AQ/965,97* C. greve/VS,

INVENTOR.

rmeln/ey:

United States Patent O 3,391,733 THERMAL PRGCESSOR Norbert J. Stevens, 12%8 N. Atmausor, Alhambra, Calif. 91801 Continuation of application Ser. No. 355,174, Mar. 27, 1964. This application Dec. 2, 1966, Ser. No. 599,345 l?, Claims. (Cl. 16S- 86) ABSTRACT OF THE DISCLQSURE Materials processing equipment accomplishes heat transfer with fluent material as it is moved through the apparatus. Hollow disc-shaped members are tilled with a heat transfer medium and are rotated in the bed of fluent material. The discs are mounted on shafts extending transversely to the direction of material movement and as they rotate mix and agitato the material to keep it at an even temperature as the material is moved along by the rotation of the discs.

This application is a continuation of application Ser. No. 355,174, led Mar. 27, 1964, now abandoned.

The present invention relates generally to equipment for processing one or more materials; and is more especially related to equipment effecting a heat transfer with a material, either for heating or cooling the material, in order to process the material in a desired fashion. The heat exchange may be for the purpose of drying the material, effecting a chemical change in the material, or for any other desired purpose.

Materials particularly suited for processing in equipment of the type herein described are dry materials which are powdered or granular in forma having a suiiiciently high degree of subdivision that they may be described generally as liuent. However, a material having the physical characteristics of a paste or a thick slurry may also be processed; but gaseous or liquid materials are not materials which it is contemplated will be handled in this type of equipment.

In process equipment embodying the present invention, it is a basic objective to obtain rapid and even heating or cooling of the material being processed. For example, assuming that the material is to be heated, it is desired to avoid any localized hot spots at which temperatures harmful to the material may be developed; and likewise also cold pockets of material are to be avoided as they may represent portions of the material which are not adequately processed.

It is also a general object of the invention to provide a processor in which the material being treated is advanced smoothly and continuously through the processor without any wide fluctuations in speed. A smooth flow of material is desired in order to avoid any impact of the particles upon each other or upon the walls or portions of the processor that degrades the particle size of the material. This is particularly important in the case of weak or triable materials which tend to produce an undesired amount of dust or powder.

A further object is to provide a flexible design for a thermal processor in order that the equipment may serve many different purposes and be able to handle many different types of materials with only minor changes. This gives the advantage of allowing standardization oi many of the parts while still making it a relatively simple matter to change the size, shape, or arrangement of the components, using standard parts, as may be required to change capacity or adapt the equipment to specialized conditions.

A further `object of the invention is to achieve simplicity of design. This is very often diiiicult of attainment ICC but is of extreme importance in producing a commercially successful design of processor since it is the basis of low capital cost of the equipment and of reliability in operation.

These objects of the present invention have been achieved in a thermal processor comprising a housing having spaced openings tor material inlet and outlet, one or more hollow shafts mounted for rotation within the housing about axes extending across the path of material tlow as it moves from said inlet to said outlet, a plurality of hollow discs spaced apart along and attached to each of said shafts, means for driving the shafts in unison, and means for circulating a liuid heat transfer medium through the shafts and discs. In an exemplary embodiment of the invention, the housing has a horizontal extent, with the inlet at one end and the material outlet at the other end. A plurality of outwardly projecting vanes are located around each of the discs for advancing material towards said outlet as the discs rotate.

In a variational embodiment, the housing is arranged with its longitudinal axis upright and as `a result, the ilow through the housing from material inlet to outlet is substantially entirely under the influence of gravity.

In either embodiment of the invention, the means for circulating the fluid heat transfer medium includes a first pipe inside and concentric with a hollow shaft and rotating therewith and a plurality of pipes each extending radially outward from the rst pipe into one of the discs and terminating near the rim of the disc. A second set of radial pipes extending from the interior of the disc into the hollow shaft allows circulation of the fluid from the rst pipe into the discs and returning through the hollow shaft; or a reverse path may be followed if desired. A rotary joint is applied to one end of the rotating shaft and pipe to provide a connection to stationary conduits which supply and remove the heat transfer medium.

How the above and other objects and advantages of the invention are attained will be more readily understood by reference to the following description and to the annexed drawing, in which:

FIG. 1 is a plan view of a thermal processor embodying the present invention, with portions of the housing broken away.

FIG. 2 is a side elevation thereof, with portions of the housing wall broken away.

FIG. 3 is a vertical transverse section as on line 3 3 of FIG. 2,.

FIG. 4 is a diagrammatic longitudinal section showing a variational drive and arrangement of discs.

FIG. 5 is a plan view of a variational form of the invention designed for vertical ow by gravity.

FIG. 6 is an end elevation of FIG. 5.

FIG. 7 is a side elevation of FIG. 5 with portions of the housing broken away.

Referring now to the drawing, and particularly to FIG. l, there is shown therein an exemplary form of the invention having a housing indicated generally at 1) which typically is rectangular in plan and also in cross-section, as may be seen in FIG. 3. This housing is :here shown as being made of metal, lalthough the invention is not necessarily limited thereto since rany suitable material may -be used. Likewise, a plain housing is illustrated; but it will be understood that it frequently will be enclosed with insul-ating material in order to aviod excessive heat losses if the material being processed is maintained at a temperature substantially above ambient.

The longitudinal axis of housing 10 is generally horizontal. At one end of the housing isa material inlet opening 12, while at the other end is a material outlet 14. Inlet 12 is in the top wall 15 of the housing and is adapted to receive material from any suitable source, not

shown, while the outlet 14 is in the 'bottom wall 16 and is adapted to gravity discharge of the material, after processing, into any desired receptacle o r other piece of equipment, not shown. In addition to the t-op wall 15 and bottom w-all 16, housing comprises a pair of vertically extending side walls 17 and end walls 18. Housing 10 is here illustrated as fully enclosed as would `be the case when it is desired to operate under an internal pressure; but it will be understood that the invention is equally applicable to an open housing similar to the `housing lil` but with top wall omitted.

Rotatably mounted in suitable bearings carried by opposite side walls 17 are a plurality of hollow shafts 22 which extend transversely across the housing interior with their axes substantially horizontal. Thus shafts 22 are adapted to rotate about axes which extend across the path of material passing through the housing from inlet 12 to outlet 14. The number of hollow shafts may be increased or decreased from that shown, as may be determined by the type of material being processed and the results desired.

Attached to each shaft 22 in order to rotate therewith is a plurality of hollow discs 24 which are spaced apart axially along the shaft 22 on which they are mounted. These discs are preferably relatively thin at the rim and thicker at their center where they are attached to the shaft 22 in order to provide adequate interior volume for circulation of the fluid heat transfer medium, as will become apparent. The two walls of each discs are slightly curved with their convex sides outward; but any other suitable shape desired may be given to these side walls. The discs have a high ratio of surface area to volume.

Any desired type of drive means may be employed to rotate shafts 22 and discs 24 thereon. As an example of a suitable drive means, there is shown electric motor 26 which drives speed reducer 27 through belt 2S. The output of the speed reducer is connected by a chain or belt 29 to a driven pulley 30 which is mounted on the projecting end of one of the hollow shafts 22. Typically, this shaft may be one near the center of the apparatus. The shaft 22 has attached to it also two drive sprockets 32, as maybe seen in FIG. l. Each of the adjoining hollow shafts also has a pair of sprockets 32, one of which is connected to the first-mentioned shaft by a chain 34 and the other of which is connected by a chain 35 to the next adjoining shaft. In this way, each shaft is driven lby an adjoining shaft and, in turn, drives the next adjoining shaft in succession.

The drive means as just described revolves all of the shafts 22 in unison; but there is no requirement that they all be revolved at the same speed, although this is usually the case, especially with discs 2.4 all the same diameter. However, there may be `situations in which it is desired to rotate sorne of the shafts faster than others, particularly those near the outlet end in order to facilitate discharge of the material from the housing. Another situation in which a differential speed may be desired is one in which the material being processed undergoes a change in volume as it moves through the housing and consequently a differential speed of the shafts is used to compensate for this change in volume.

Hollow discs 24 are primarily movable members carrying heat transfer surfaces for the purpose of effecting a transfer of heat between these members and the material being processed, although, as will become appare-nt, the discs may assist in promoting movement of the material through lthe housing. Discs 24 are hollow in order to receive, and to form a part of the circulation path of, the lluid heat transfer medium. This heat transfer medium is introduced into each of the discs through a pipe 38 which extends radially into the disc through the wall of shaft 22 and `terminates preferably near the outer rim of the disc, as shown in FIG. 3. The inne-r end of each radially extending pipe 38 is in communication with pipe 39 which is mounted in and concentrically with hollow shaft 22.

Pipe 39 is mounted within the shaft in such a fashion that the pipe turns with the shaft.

At one side of housing 10, both shaft 22 and pipe 39 extend outwardly through a side wall 17, as may be seen in FIG. 3, where they are attached to a rotary coupling 40 which may be of any one of various well-known designs adap'ted to effect a fluid-tight connection between passages within the stationary part of coupling 40 and the fluid spaces within the rotating pipe and shaft. For this purpose, coupling 40 is attached to inlet pipe `41 which is connected to a header 42, which serves as a common conduit to supp-ly heat transfer medium to all of the shafts in the housing. Thus the heat transfer medium er1- tering 4through pipe 41 ilows into pipe 39 through the rotary joint and thence through the radially extending pipes 38 in the individual discs carried by the shaft.

-From the interior of each disc, the fluid flows back into the hollow interior of shaft 22 through a second radially extending pipe 43 carried by shaft 22, each pipe 43 lcommunicating at one end with the `interior of a disc 24 and at the other end with the interior of shaft 22. The interior of shaft 22 thus provides a common return path lfor heat transfer fluid from all the discs, the fluid flowing out of the end of the shaft and into rotary coupling 40 from whence it leaves by pipe 44 connected to header 45 serving as a common return line for all of the shafts. In a usual situation, the fluid heat transfer medium is heated before entering the processor and this may be accomplished in any type of heater or furnace, not shown in the drawings since this piece of equipment `forms no part of the present invention. However, it will be understood that the header 42 and the header 45 are connected by suitable piping to such heater or furnace in order that they may respectively receive and return the fluid heat transfer medium to or from the furnace, as may be the case.

Radial pipes 43 rotate with shaft 22 and so sweep across the top of the interior space of each disc once a revolution. Thus they are able to `discharge any vapor trapped in the discs above liquid therein, assuring adequate fluid circulation at all times. j

Taken by themselves, discs 24 exert very little or no conveying action on the material being processed. There is a frictional drag between the disc surfaces and the contacting material as the discs turn in the body of material being processed; but this alone is not sufficient to advance the material through the housing. However, because of this drag, the discs all turn in the same direction so that the lower half of each disc is moving in the direction of material flow between inlet 12 and outlet 14. In other words, the discs are all turning counterclockwise viewed in FIG. 2.

Conveying movement is imparted to the material by a plurality of small plate-like vanes attached to each disc around its periphery. These vanes 48 are small pieces of plate which extend outwardly from the outer surface of the discs, preferably, but not necessarily, extending axial- 1y of the discs as shown in FIG. 3. The vanes are preferably arranged so that some project from one side of the disc and some from the other, thus giving a greater effectiveness to a given number of vanes, the number being determined by the speed of rotation of the discs and the speed with which it Vis desired to move the material through the housing.

When the average depth of material in the housing is about half the diameter of the discs, these vanes are effective to exert a conveying action on the material only during half of the revolution of the disc, more particularly the lower half of each disc revolution where the movement of these vanes is in a direction to advance the material toward outlet 14. However, the vanes exert a net advancing motion even when the material depth fully submerges the discs -at the inlet end. Not all discs are fully covered as the surface of the material recedes from the outlet at some angle of repose determined by the physical properties of the material. Even where the axis of the housing yis horizontal there is some assistance to material lflow from gravity, and this may be increased by sloping the axis downwardly toward the outlet.

In order to improve the conveying action of vanes 48, it is preferred that the bottom wall of the apparatus on which the material being processed rests is not planar but is rather a series of arcuate surfaces 50 concentric with the successive axes of the successive shafts 22, as shown particularly in FIG. 2. These arcuate surfaces 50 are closely spaced from the paths of vanes 48 so that throughout its travel through 4the housing, the material being processed rests upon a surface which is at all times closely and relatively uniformly spaced from the path of the vanes which act to advance the material through the housing.

The effect of vanes 48 can be controlled by varying any one or more of various design features, as number, size, and inclination of the leading face of the vanes.

The foregoing description assumes a continuous material flow through the apparatus. In the event that the apparatus is used for processing by batches rather than for continuous ow, the vanes 4S may be omitted since there is no need for `conveying action. These vanes may likewise be omitted in the event that flow of material through the apparatus is substantially entirely by gravity, as in the form of the invention subsequently described.

It will be noticed from FIG. l that the spacing between successive shafts 22 is less than the diameter of discs 24 and that the discs on one shaft are laterally offset from those on the next successive shaft. This permits the discs on any one shaft to intermesh with the discs on the adjoining shaft or shafts, an arrangement which has several advantages. The degree of overlap of the discs on one shaft with those on the next depends upon several factors but is preferably made as much as possible within the configuration of the shafts and discs. A minimum overlap of the discs on two successive shafts in order to obtain the advantages hereinafter described is one-half the maximum radius of the discs, but the design illustrated permits an overlap a-mounting to approximately 70 percent of the radius of the discs. Obviously, a limiting factor in this overlap is the outside diameter of shafts 22.

Intermeshing or overlapping discs 24 as `described improves the action of vanes 48 in advancing the material through the processor since thereby the vanes on one shaft are able to adv-ance the material into the zone of action of the vanes on the next successive shaft.

Intermeshing the discs permits a larger number of discs to be used within a processor housing of a given size. In turn, this increases the ratio between the number of square feet of heat transfer surface available to the volume of material being processed. It is obvious that, in order to obt-ain a high heat transfer rate, the maximum possible amount of surface available for heat transfer is desired in proportion of a given volume of material. For this same reason, the discs are made relatively thin axially and long radially, compatible with adequate circulation of heat transfer fluid within them, and are also closely spaced along each shaft 22, while allowing intermeshing since the major portion of the total heat transfer surface available is on the discs, the shaft periphery furnishing only a small portion of the total heat transfer surface.

With the overlapping relation shown, the space between two discs on one shaft is occupied in part by discs from one or two adjoining shafts. This enables the designer to obtain a very high ratio of heat transfer surface to volume treated. Depending upon various factors, such as the dimensions of the discs, the number, the length-to-width ratio of the housing, and other physical factors, it is possible to achieve at Eleast 5 square feet of heat transfer area per cubic foot of material bein-g processed, and in some designs, this can be increased to as high as l5 to 17 square feet per cubic foot of material treated.

A further advantage of the inter-meshing is the reduction in the mean path heat must travel 'from a surface to thoroughly heat or cool the material. Without overlapping, the mean path is half the average distance between two discs on the same shaft; 'but with overlapping as shown, in the area of overlap the mean path is reduced to onehalf the spacing between discs on successive shafts. It will be apparent from inspection of the drawings that this latter `distance maybe of the order of only approximately one-fourth of the former distance. Hence, with this arrangement, much of the material is between two relatively closely spaced heat transfer surfaces, with the result that heat transfer to all .portions of the material is effected quickly and easily.

Intermeshing of the discs also is advantageous from the standpoint of agitating the material gently for the purpose of bringing all of it into a desirable heat transfer relationship with respect to the surfaces of the discs but without handling the material in a manner to degrade particle size. The shearing stresses produced in the material within the area of overlap between two successive discs, where the discs are moving in opposite directions, cause particle relocation in a highly desirable manner that effects quick heating or cooling without grinding or abrading the particles and thus `breaking down their size or changing their physical characteristics.

FIG. 4 illustrates diagrammatically some possible changes in the drive and in the arrangements of discs in the processor described above. Two of the shafts 22s carry discs 24s of smaller diameter than the others. These two shafts are driven clockwise, opposite to the other shafts. The drive sprocket at 32s isl larger than the sprocket 32 so that the speed of rotation of these two shafts is less than for the others. This drive arrangement causes successive or adjoining shafts to turn at different speeds and in opposite directions.

In thi-s form of processor, the materia-l travels more slowly from inlet to outlet and so residence time is increased for a given length of housing. Compare, for example, with FlG. 2. Also, in the zones of overlap there is more mixing action than in the first-described arrangement. The lower speed and smaller diameter allow the vanes on 'the full :size discs to predominate in their effect on the material, hence they advance the material toward the out-let, as before, but more slowly.

FIGS. 5, 6 and 7 illustrate a variational embodiment of the invention which is constructed in its essential aspects in the same manner as previously described but is adapted to gravity ow through the housing. Corresponding parts have been indicated by the some reference numerals as before except that the suix a has been added to each reference numeral.

In this embodiment of the invention, the housing axis and ow through the device are in a generally vertical direction and, accordingly, the inlet 12a is at the top of housing lila, while the material outlet 14a is at the bottom. Vanes 48 are not necessary for advancement of the material which advances under Ithe influence of gravity and, therefore, are omitted in this embodiment. Likewise the arcuate walls 50 may be omitted and all interior walls made essentially planar.

Discs 24a are arranged in four tiers of two shafts each, with the tiers arranged one above another. Hence, the material flow is from the discs of one tier tothe discs of the other tier below it and normally flows in a zig-zag path as it lpasses around the discs in succession.

FIGS. 6 and 7 illustrate an optional arrangement in which one or more nozzles are added. Air under pressure is forced out of small openings in the underside of the nozzles to iluidize the mass of material passing through the housing. The air not only iiuidizes the material but dries it. A gas other than air may 'be used if desired to obtain intimate contact with -such gas and the material to promote drying, cooling, or a chemical reaction while the material is in the housing.

It is evident that various changes in the construction and arrangement of the apparatus may occur to persons skilled in the art without departing from the spirit and scope olf the invention. For exam-ple, the longitudinal axis of the housing can be inclined instead of longitudinal or horizontal. Also vario-us arrangements of the shafts and discs may 'be used to balance total through put against residence time, as desired. Hence, the foregoing description is considered to be illustrative of, rather than limitative upon, the invention as defined by the appended claims.

What is claimed is:

1. A heat transfer apparatus comprising:

a housing defining an enclosure -for supporting and maintaining a body of fluent granular material in a bed on the lower surface thereof, said housing having a material inlet and a material outlet spaced therefrom in communication with said enclosure;

a plurality of parallel spaced hollow shafts mounted for rotation within said enclosure about horizontal axes extending transversely across said bed of material between said inlet and said outlet;

a plurality of hollow discs attached to the shaft centrally of the discs and extending radially outward from the shafts, the discs being spaced apart axially along each of the shafts and extending partly into said bed of material;

means for circulating a uid heat transfer medium through the shaft and discs;

`drive means for rotating the shaft and discs to thereby impart movement in said bed from said inlet to said outlet;

and means carried by at least some of said discs on each of said shafts for mixing the body of fluent material;

2. An apparatus in accordance with claim 1 wherein said last mentioned means comprises means carried by and projecting from each of said discs to increase movement imparted by rotation of said discs.

3. An apparatus in accordance with claim 2 wherein said means carried by said discs comprise a plurality of outwardly projecting vanes around each disc to mix and to advance the uent material toward said outlet as the discs rotate.

4. An apparatus as claimed in claim 1 in which the drive means includes means driving said shafts at different rotational speeds, shafts nearer the outlet being rotated faster than shafts remote from the outlet.

5. An apparatus as claimed in claim 1 in which each disc is circular and is concentric with the shaft on which the disc is mounted.

6. An apparatus in accordance with claim 1 wherein the means to circulate the heat transfer medium includes:

a first pipe inside and concentric with the hollow shaft and rotating therewith; and

a plurality of pipes each extending radially from said first pipe into one of the discs and terminating near the rim of the disc.

7. An apparatus as claimed in claim 1 in which the discs on successive shafts overlap each other.

8. An apparatus as claimed in claim 7 in which the Ihousing has longitudinally extending side walls and discs on some shafts are spaced from said side walls to permit overlap of discs on adjacent shafts.

9. An apparatus in accordance with claim 7 wherein the means to circulate the heat transfer mediu-m includes:

a first pipe inside and concentric with the hollow shafts and rotating therewith; and

a plurality of pipes each extending radially from said first pipe into one of the discs and terminating near the rim of the disc.

10. An apparatus in accordance with claim 7 which also includes a plurality of outwardly projecting vanes around each disc to mix and to advance the fluent material toward said outlet as the -discs rotate.

11. An apparatus in accordance with claim 7 wherein discs on successive shafts overlap each other by more than one-half the radial extent of the discs.

12. An apparatus in accordance with claim 11 in which the ratio of heat transfer surface on the shafts and discs to the volume of material space is greater than about 5 square feet per cubic foot of material space in the hous- 13. An apparatus in accordance with claim 7 in which the material inlet is at the top of the housing and the material outlet is at the bottom, the inlet and outlet being also horizontally spaced apart.

References Cited UNITED STATES PATENTS 2,731,241 l/1956 Christian -87 3,020,025 2/1962 OMara 165--87 1,253,347 l/l9l8 Campbell 165-91 3,022,046 2/1962 Breig 165--90 ROBERT A. OLEARY, Primary Examiner.

T. W. STREULE, Assistant Examiner. 

